I. Basic Concepts of Distribution Boxes
The distribution box is a core device in the power system used for centralized distribution of electrical energy, control of circuits and protection of electrical equipment. It distributes electrical energy from power sources (such as transformers) to various electrical devices and integrates protection functions such as overload, short circuit and leakage.

Main uses:

Distribution and control of electric energy (such as power supply for lighting and power equipment).

Circuit protection (overload, short circuit, leakage).

Monitor the circuit status (voltage and current display).

Ii. Classification of Distribution Boxes
By application scenarios:

Household distribution box: Small in size, with a relatively low protection level, integrating leakage protection, air switches, etc.

Industrial distribution box: Large capacity, high protection level (IP54 or above), supporting complex circuit control.

Outdoor distribution box: Waterproof and dustproof (IP65 or above), suitable for open-air environments.

By installation method:

Exposed installation type: Directly fixed to the wall, easy to install.

Concealed type: Embedded in the wall, it is aesthetically pleasing but the construction is complex.

By structural form:

Fixed type: Components are installed in a fixed manner, with low cost.

Drawer-type (modular distribution box) : Modular design, convenient for maintenance and expansion.

Iii. Composition Structure of Distribution Boxes
Box body:

Material: Metal (cold-rolled steel plate, stainless steel) or non-metal (engineering plastic).

Protection level: IP codes (such as IP30, IP65) indicate dust and water resistance capabilities.

Internal electrical components:

Circuit breakers: Overload/short-circuit protection (such as air switches, molded case circuit breakers).

Disconnector: Manually cut off the power supply.

Leakage protection device (RCD) : Detects leakage current and trips.

Electricity meter: Measuring electric energy.

Contactor: Remotely controls the on and off of the circuit.

Surge protector (SPD) : Protects against lightning strikes or overvoltage.

Auxiliary components:

Busbars (copper or aluminum busbars), terminal blocks, indicator lights, cooling fans, etc.

Iv. Technical Parameters of the distribution box
Rated current: such as 63A, 100A, 250A, which should be selected based on the total power of the load.

Rated voltage: Commonly 220V (single-phase) or 380V (three-phase).

Protection grade (IP) : such as IP30 (dust-proof), IP65 (water-proof).

Short-circuit endurance: The time to withstand short-circuit current (such as 10kA/1s).

Breaking capacity: The maximum fault current that a circuit breaker can safely cut off.

V. Selection Guide for Distribution Boxes
According to the load type:

Lighting circuit: Select a 10-16A miniature circuit breaker (MCB).

Motor equipment: Thermal relays or motor-specific circuit breakers need to be matched.

High-sensitivity areas (such as bathrooms) : A leakage protection device (30mA) must be installed.

Capacity calculation

The total current is ≤ the rated current of the distribution box × 0.8 (safety margin).

For example, the total load power is 20kW (three-phase), and the current is approximately 30A. It is recommended to choose a 50A distribution box.

Environmental adaptability

Humid environment: Choose stainless steel box body + high protection grade (IP65).

High-temperature environment: Heat dissipation holes or fans are required.

Extended requirements:

Reserve 20% of the empty space to facilitate the addition of new circuits later.

Vi. Installation and Maintenance Precautions
Installation requirements:

The location is dry and well-ventilated, away from flammable materials.

The box is reliably grounded to prevent the risk of electric leakage.

Wire color specifications (live wire red/yellow/green, neutral wire blue, ground wire yellowish green).

Maintenance key points:

Regularly check whether the wiring is loose or oxidized.

Clean the dust (to avoid short circuits).

Test the protection device (such as pressing the leakage protection test button once a month).

Vii. Common Problems and Solutions
Frequent tripping

Cause: Overload, short circuit or leakage.

Troubleshooting: Disconnect the load line by line and locate the faulty circuit.

Tripping of the leakage protection device

Possible: Damaged insulation of the circuit, leakage of electricity from the equipment.

Treatment: Use a megohmmeter to test the insulation resistance.

The box is overheating.

Cause: Overload or poor contact.

Solution: Reduce the load or tighten the terminal blocks.

Viii. Safety Regulations
It must comply with national standards (such as GB 7251.1-2013 “Low-voltage Switchgear Assemblies”).

When installing and maintaining, power must be cut off and the operation should be carried out by professional electricians.

It is prohibited to modify the internal circuits at will or remove the protective devices.